Down Syndrome: New Rules Recommended for Prenatal Screening

On May 17, 2017, the French National Health Authority published an updated list of recommendations to screen for Down syndrome (Trisomy 21) during pregnancy. They specify the role and the conditions for performing new tests on fetal DNA circulating in the mother’s bloodstream.

A blood sample from the mother is tested for the presence of the baby’s genetic fragments. This is a “screening” technique, and not a “diagnosis” for Down syndrome since many potential errors remain. Only amniocentesis or trophoblast biopsies are reliable diagnosis methods which can verify or contradict the screening test result.

In 2015, following the Health Minister’s referral, the National Health Authority had already evaluated the performance of the tests. Today the recommendations for performing the screening test are specified. The purpose is to give pregnant women or couples the most reliable information possible for the risk of Down syndrome, and decrease having so-called invasive procedures performed which are needed to confirm the diagnosis.

During the first term, three criteria risks are used to evaluate the risk: a blood test for serial markers, a sonogram to measure the fetus’ nuchal translucency and the mother’s age.

The new screening test will be proposed as a complementary procedure for women whose risk is evaluated at 1 in 1000 versus the current proposition of performing amniocentesis when the risk is 1 in 250. Thus twice the number of women would be tested using this intensified screening technique. The National Health Authority estimates this will detect 15% more infants with Down syndrome, whereas the number of fetal karyotype exams by amniocentesis would decrease by 25%.

However, amniocentesis would only be proposed to women with a risk of 1 in 50, compared to previously when the risk was 1 in 250.

As a reminder, in 2014, approximately 18,500 pregnant women with a risk above or equal to 1 in 250 had “fetal karyotype” exams. The diagnosis of Down syndrome was only confirmed in approximately 750 of these cases.

By the decree dated May 5, 2017 in the French Official Journal, non-invasive prenatal testing (NIPT) was added to the list of screening tests for Down syndrome during pregnancy. The Paris Public Hospital Network has already announced it will incorporate this screening test throughout its sites for at-risk pregnancies.